Introduction to gbase 8s storage structure and space management

        Gbase 8s Instances can create multiple dbspace, One dbspace Can contain multiple physical chunk, One chunk Divided into multiple continuous expansion areas extent, The space occupied by a table or index is called a tablespace, One extent Contains multiple physical pages page.[ among dbspace、tablespace and extent Belongs to logical storage unit ;chunk and page Belongs to physical storage unit ]

Physical storage unit ：

1. chunk： Continuous disk space for storing data , That is, files or raw devices that store database data , The biggest can be 4TB.
2. page: Is the minimum sum of the basic storage units I/O unit . A data page is divided into three parts ： Header 、 Footer and data section , The total number of page headers is 24byte Space , It consists of eight parts . The footer consists of two parts ： Timestamp and each slots Description information of .

Logical storage unit ：

1. dbspace： It's one or more chunk Logical set storage unit , The logical storage unit of the database table With physical storage units chunk come together .
2. tablespace： It 's a logical concept , Refers to the space occupied by a table or index .
3. extent： A collection of physically contiguous data pages ,tablespace（ Tables and indexes ） The storage space is extent Assigned as a unit . for example , In the custom Continuous in the table insert When recording , Is a table customer The allocated space will be used up , here , The database needs to expand new space for tables ,gbase 8t With extent Expand by , One extent Contains several physically contiguous data pages .

Large object storage ：

1. Simple large objects ：blobspace It can only be used to store simple large object data . Simple large objects can be stored in dbspace perhaps blobspace in . There is dbspace The method of writing to the disk is the same as that of ordinary table data , That is, cache the data in the shared memory first buffer in , Then refresh to disk , Record logic at the same time 、 Physical log information . If the specified object is large, it will be stored in blobspace On , The virtual segment will use a smaller cache to write data directly to disk , similar light-append The way , Without taking up a lot of buffer-pool Memory space , This avoids squeezing other tables or indexes out of memory , At the same time checkpoint No influence , Moreover, the log information of the data is not written to the logical log 、 Physical log file . All use one 56byte Pointer to the storage location information of the large object .

2. Intelligent large objects ： Smart large objects must be stored in sbspaces On , Storage structure and structure of intelligent large objects I/O Behavior by sbspace Characteristic determination .sbspace One of the first chunk It always consists of three parts ： Metadata area 、 User data area and reserved area , other chunk You can share the first chunk The metadata area of . The metadata area holds metadata , Used to represent sbspace Key information and stored in the sbspace Every smart big object on the , In this way, the database server can operate and recover intelligent large objects . The user data area stores user-defined smart large object data , One chunk There can be 1-2 A reserve . When metadata area and user data area need more space , Can be allocated from a reserved area , One chunk There can be 1-2 A reserve . The database server uses shared memory buffer pool To access smart big object data , And stored in dbspace The data on is the same . However, the memory priority of the user data part in the intelligent large object is low , When writing data , When one buffer page When filled , Write to disk now .

Gbase 8t Storage limits ：

When we look into the table insert When recording , Problems and solutions ：

· The space is insufficient -> Expand the space

·extents Maximum upper limit -> Rebuild table , Use larger extend size and next size Or delete some records in the table

· Maximum data page limit -> Use a shard table or use a larger data page